US broadcaster NBC has claimed "phenomenal" ratings for its multimedia coverage of the 2008 Beijing Olympics, with viewing figures bolstered by on-demand, web and mobile content.

In the first four days of the event, the official broadcaster for the Olympics across the US saw viewing peak on Sunday with Michael Phelps' second gold of the games during the 4x100 mens' relay.

NBC, which has been using a new measurement system to combine viewing figures across all media outlets, saw TV viewing peak at 107.3 million across the US that night, up from 70.1 million on Friday.

Though TV still accounts for the vast majority of Olympic viewing, its share dropped the following Monday from 95% to 92% as the volume of online viewing of NBC's Beijing coverage grew.

The NBC website saw unique user numbers increase from 4.2 million last Friday, August 8, the first day of the games, to 7.8 million on Monday, August 11, when viewers wanted to replay Phelps' US swimming victory. NBC recorded 1.7 million downloads of the final 4x100 relay final.

In the UK, BBC Sport Interactive head Ben Gallop said bbc.co.uk recorded more traffic in the first two days of the games than in the entire two weeks of the 2004 Athens games.

Commenting on the record traffic, Gallop described Beijing as "a stepping stone for London - we want try things out and see how they work to learn for four years' time".

Alan Wurtzel, research president for NBC Universal, said the ratings are well ahead of the Athens games in 2004 and confirmed that the 2008 Beijing Olympics are the most viewed ever, with 114 million US viewers compared with 110 million for Athens.

Wurtzel also said the broadcaster has been "stunned" by the popularity of mobile content. On August 8 just 210,333 people accessed the NBC service, but by Monday this had more than doubled to 476,062.

More than half these people are accessing mobile content for the first time, NBC research found.

"These Olympics are influencing how people are using new technology," Wurtzel said. "Half of the people viewing on mobile are using it for the first time. After the Olympics, it will be interesting if these habits become part of their behaviour."

On top of TV coverage, NBC is offering an unprecedented 2,200 hours of live Olympic webcasts and 700 hours of additional, exclusive content distributed through cable TV, although some commentators have criticised NBC's decision not to post any events online until they have been aired on TV.

Wurtzel also admitted that NBC had feared that online content would cannibalise the TV audience, which is the most lucrative for advertising - but said this has not been the case. NBC's research showed that just 0.2% of its audience used the web exclusively.

"The internet hardly cannibalises - it actually fuels interest," said Wurzel, explaining that half the online viewers were watching events they had missed and about 40% wanted to see replays.

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